1. Field of the Invention
The present invention relates to a microwave oven, and more particularly to a magnetron driving control apparatus of a microwave oven and method thereof by which a magnetron is controllably driven to prevent a high voltage transformer from being over-heated without recourse to a large-sized high voltage transformer for decreasing a heat generation caused by electrical resistance.
2. Description of the Prior Art
Generally, a microwave oven is a cooking device for cooking foodstuff by way of dielectric heating of microwaves.
The microwave oven thus described includes, as illustrated in FIG. 1, a high voltage transformer 10, a magnetron 20, a waveguide 30, a cooking chamber 40, a turntable 50, a turntable motor 60, a fan 70 and a fan motor 80.
The high voltage transformer 10, in FIG. 1, converts a commercial alternating current AC voltage input from outside to a high voltage (by way of example, 2KV) appropriate enough to generate a high frequency wave, thereby applying same to the magnetron 20, where the magnetron 20 performs a high frequency wave oscillation according to the high voltage input from the high voltage transformer 10 to generate a microwave. The waveguide 30 serves to guide the microwave generated from the magnetron 20 into the cooking chamber 40.
The turntable motor 60 is operated at a low speed (by way of example, 10 rpm) by a predetermined level of voltage applied from electric power source means (not shown) to rotate the turntable 50, which is cooperatively rotated with the turntable motor 60 to evenly radiate the microwave on the foodstuff placed thereon.
Furthermore, the fan motor 80 is driven by the commercial AC voltage input from outside to rotate the fan 70. The fan 70 is cooperatively rotated with the fan motor 80 to cool the high temperature heat generated from the magnetron 20 when the magnetron 20 is rotated and to blow cool air of outside to the magnetron 20.
Operational process of the microwave oven thus constructed according to the prior art is described below.
First of all, when a cooking time set-up key at a key input unit is manipulated to input a cooking time and an output control key is manipulated to set up power output level, and a cooking start/stop selection key is manipulated to instruct a cooking start, a key signal corresponding thereto is applied to a control unit from the key input unit.
At this time, the control unit discriminates the cooking time and the output level set up by a user according to the key signal input from the key input unit and when the key signal is input from the key input unit to instruct the cooking commencement, the turntable motor 60 and the fan motor 80 are driven to rotate the turntable 50 and the fan 70.
When the output level established by the user is discriminated as a maximum value, the control unit continuously supplies to the magnetron 20 the high voltage generated from the high voltage transformer 10 during a cooking time established by the user.
At this time, microwaves are continuously generated from the magnetron 20 according to the high voltage continuously supplied from the high voltage transformer 10 to be supplied into the cooking chamber 40 via the waveguide 30, thereby cooking the foodstuff placed on the turntable 50 by way of dielectric heating action.
Meanwhile, when the output level established by the user is less than the maximum value (by way of example, 10-90%, in case of the maximum value of the output level being at 100%), the control unit supplies to the magnetron 20 in an off-and-on way the high voltage generated from the high voltage transformer 10 according to on/off period corresponding to the output level established by the user.
The microwaves are generated in an off-and-on way according to the high voltage intermittently supplied from the high voltage transformer 10 to be supplied into the cooking chamber 40 through the waveguide 30, such that the foodstuff on the turntable 50 is cooked by way of dielectric heating operation.
In other words, when the output level set up by the user is at the maximum value, the magnetron 20 is continuously activated, and when the output level established by the user is at less than the maximum value, the magnetron 20 is intermittently driven according to driving period corresponding thereto to thereby control an output of the microwaves.
Meanwhile, an mentioned above, when the magnetron 20 is intermittently driven according to the output level established at less than the maximum value, the high voltage transformer 10 is naturally cooled during the on/off period to thereby generate a small quantity of heat. However, when the magnetron 20 is continuously driven according to the output level established at the maximum value, a relative oven-heat is generated because there is no time for the high voltage transformer 10 to cool by itself.
At this time, according as coil temperature at the high voltage transformer 10 becomes higher, coil resistance is increased to make copper loss bigger, such that, when the high voltage transformer is over-heated by the continuous driving of the magnetron 20 as described above, the high voltage transformer 10 is deteriorated in efficiency thereof to increase a power loss and to occasionally cause a fire due to the over-heat.
Accordingly, International Electrotechnical Commission IEC has stipulated that a high voltage transformer shall not exceed a regulated temperature, such that a large-sized high voltage transformer which has enlarged the sizes of the coil diameter and core has been installed in the microwave oven according to the prior art to meet the regulations of IEC.
By way of reference, when the sizes of the coil diameter and core become larger, electric resistance becomes small to decrease a heat generation according to the resistance and subsequently to decrease the whole heat generation.
However, there is a problem in the microwave oven according to the prior art thus described in that a large sized high voltage transformer having enlarged coil diameter and core is mounted therein to meet the temperature stipulated by IEC, to thereby increase a manufacturing cost and overall weight of the product.